In designing a mobile communication system, it is very important to prevent loss of user data during handover between base stations. Especially, if data loss occurs in a real-time application such as voice or videophone communication, it is difficult to compensate for the loss by retransmission of packets and as a result, the quality of voice or video may be degraded.
In IMT-2000 that is an international standard for mobile communication systems, a soft handover method can be employed for handover between base stations. In soft handover, a mobile terminal communicates with the network via two or more base stations at the same time. Therefore, soft handover reduces the possibility of user data loss and makes it possible to perform high-quality handover. For example, patent document 1 discloses a technology for applying soft handover to a mobile station receiving and sending real-time data. However, soft handover requires multiple radio channels for each user and increases the workload of base stations controlling the handover. This in turn may complicate the system architecture and the radio communication control process and thereby increase system costs.
[Patent document 1] Japanese Patent Application Publication No. 2002-191064